Sift the flour into a bowl with a pinch of salt and add the fat, cut into small, cherry-sized pieces.
Stir well, make a well in the centre and pour in the water and lemon juice.
Mix, first with a knife, then with one hand until it forms a ball, but do not knead.
Turn on to a floured board and pat into a rectangle; if it looks impossibly messy, is sticky and has lumps of butter sticking through, you have done it right! Roll out with short, sharp strokes), so that it is three times as long as it is wide (about 39 cm X 13 cm/15 in X 5 in).
Fold the bottom third up, then the top third down over it, keeping the edges neatly on top of each other.
Let it rest for a few minutes and then gently use the rolling-pin to seal both ends and the side seam, thus trapping the air.
If you don't do this, you will be wasting at least half of your effort.
Still using the short, sharp strokes, roll and fold and rest twice more.
By this time it will begin to be recognisable as pastry.
Be generous with dredged flour on top and bottom but brush off the excess before folding and be pernickity about resting and sealing the folds each time.
Cover the pastry and chill for 10-15 minutes.
Starting with the folded edge on your left again, roll and fold as before.
If pieces of fat are still showing through, don't worry, simply dredge with more flour.
Fold, roll and turn at least once more.
Now wrap and chill for at least 30 minutes before rolling out and using.
Rough puff pastry should be baked in a very hot oven (220°C/425°F/Gas Mark 7) and may be glazed with beaten egg or painted.